For determining relative positions between two elements, a carrier having at least one barcode track and at least one sensor arrangement for detecting code information, e.g. barcodes, are used in many fields of application. The detected barcode information makes it possible to determine the sensor position relative to the code or to the code carrier, wherein, in principle, both the code carrier and the sensor can be configured as the movable unit relative to the rest of the components. When linear positions are determined, linearly running codes or graduations and sensor arrays partly overlapping the latter are used. An angular position can be detected with a circular graduation and a sensor array, in particular a CMOS array, extending over a section of the circular graduation.
Different graduations are used depending on the field of application, functional principle and accuracies to be realised. By way of example, a circular graduation can be divided into intervals encoded in an absolute fashion, wherein the sensor array reads the interval number and derives a coarse angle determination therefrom. In order to obtain an exact angle value, the position of an interval mark relative to the sensor array is determined from the intensity values of the sensor array.
The documents EP 0 085 951 B1, U.S. Pat. No. 4,668,862 A1 and DE 199 39 643 describe different solutions for position determination. In accordance with EP 0 085 951 B1, the centroid of the interval mark is determined. U.S. Pat. No. 4,668,862 A1 additionally describes the determination of a line pattern characterizing the respective interval. In DE 199 39 643 A1 the position of the interval mark is determined by means of the flank positions of many graduation lines being detected and a single fine value being determined therefrom.
DE 35 28 955 A1 discloses an angle measurement for geodetic instruments, wherein a rotatable pitch circle comprises both a graduation encoded in an absolute fashion and an incremental graduation. The angle magnitude is determined from the two graduations being read by means of two fixed sensor systems diametrically opposite one another and by means of two rotatable sensor systems diametrically opposite one another. The outlay for the two reading processes is high and reading errors can nevertheless occur.
If the center of the circular graduation does not lie precisely in the center of the rotation axis, then eccentricity errors occur, which can be corrected for example in accordance with various exemplary embodiments in EP 1 632 754 A1. This solution is only directed to the eccentricity and cannot minimize other errors.
EP 325 924 A1 and DE 199 07 326 A1 describe a determination of the angular position using four scanning sensors, wherein eccentricity errors are reduced by the signal evaluation of the four scanning sensors.
The quality of a position determination can also depend on the transmission of the signals determined by the scanning sensors. DE 34 45 617 A1 describes a serial transmission of measurement value data with transmission rates of 1.5 to 2.0 MHz. Precisely with high transmission rates, errors can also occur depending on the sensor arrays used.
Since the measurement accuracy is also dependent on the light intensity, U.S. Pat. No. 7,291,831 B2 and U.S. Pat. No. 7,291,831 B2 describe solutions wherein the brightness of the light source is adapted in accordance with an intensity measurement. U.S. Pat. No. 6,483,104 B1 describes the use of pulsed light in order to overcome problems with short scan times and weak light. Complex light sources and controllers have to be used for high light intensities at high pulse rates.